The invention relates to a hose cassette for a peristaltic pump, comprising a cassette housing, a flexible hose extending through the cassette housing, the hose being guided in the cassette housing along a circular segment and the cassette housing having a cutout for the engagement of a roller wheel of the peristaltic pump into the interior of the circular segment, arid comprising connection elements for connecting the cassette housing to the peristaltic pump. The invention further relates to a peristaltic pump comprising such a cassette. Hose cassettes of the type mentioned above are in particular used as sucking and rinsing pumps for medical applications. Insofar the hose may perform the function of a rinsing or a sucking line. Examples for medical applications are the arthroscopy, the hyteroscopy and the cystoscopy. For medical applications, particularly sterility satisfying all requirements, is important, and therefore the hose is normally disposed of after an application, so to avoid cross contamination between different patients. The hose cassettes have thus to be economic to make, on one hand, and to permit simple handling, on the other hand.
As to prior art peristaltic pumps, there are in principle two different basic configurations. The first basic con figuration consists in that the hose disposed around the roller wheel is pressed against the roller wheel by means of a pressure bracket or the like. Such embodiments are for example known from documents U.S. Pat. No. 4,798,580 and U.S. Pat. No. 5,044,902. Of a substantially similar mode of operation is the subject matter of document U.S. Pat. No. 4,798,580, according to which a cassette with a pressure bracket is provided behind the hose. The cassette is fixed by a lever closure mechanism, and simultaneously the hose is pressed by the pressure bracket against the roller wheel at the pump housing. In the subject matter of document U.S. Pat. No. 5,044,902, the roller wheel is integrated in the cassette, and when mounting in the cassette, the hose is pressed towards the cassette wall and against the latter by centering the roller wheel on its guiding portion.
The second basic configuration, on which the invention in principle relies, consists in that the hose is pulled with sufficient enclosing angle around the roller wheel by a tensional force of suitable size. Hereby a pressure bracket or the like will not be needed. The tensional force has to be adjusted, according to the elastic properties of the hose, such that in the area of a roller of the roller wheel, the inner cross section of the hose is reduced to virtually zero. Examples can be found in documents U.S. Pat. No. 4,537,561 and U.S. Pat. No. 5,213,483. In the insofar prior art embodiments, the hose is fixed at opposite ends of the cassette and extends in a straight line between such ends. The cassette is then pressed on in a radial direction, in relation to the roller wheel, towards the roller wheel and is fixed with suitable fixing elements. Hereby, by dimensioning the geometry of the cassette and of the connection elements according to the elasticity of the hose, a tensional force on the hose portion interacting with the roller wheel and meeting the requirements will be achieved; handling is however relatively complicated, and it is regularly necessary to use both, hands for putting the cassette in place. This is also caused by that the forces required to press the cassette on may be rather substantial, and some finesse will be required for precise positioning by manual operation against these forces.
In contrast thereto, the invention is based on the technical object to provide a hose cassette and a peristaltic pump permitting connection of the cassette to a pump housing in a particularly simple and handy manner.
For solving this object the invention teaches that at least one hose leg to be connected to the circular segment is displaceably held between a mounting position and an operating position in the cassette housing. Displaceability may be provided in a straight line or along a curve. The basic concept of the invention consists in that in a first mounting step, the cassette with the hose leg being in the mounting position is put in place at a pump housing, and in a second mounting step, by pulling at the displaceable hose leg, the hose will rest against the roller wheel with the required pressure. This is then the operating position of the hose leg. Hereby it is achieved that the hose cassette can in a simple way be mounted at a pump housing, and that without counter pressure from elastic forces of the hose. The cassette can thus easily be mounted with one hand. Immediately thereafter the required pressure of the hose around the roller wheel with sufficient tensional force is adjusted by a simple pull at the displaceable hose leg. It is understood that the displaceable hose leg is fixable in a suitable manner in the operating position, for example by latching. For this, too, one hand only is required, since the weight of the peristaltic pump generates sufficient counter force against the elastic forces of the hose.
It is preferred to adjust the operating position by that, when the cassette is mounted at the peristaltic pump, the displaceable hose leg is adjustable by pulling at the hose portion immediately following the displaceable hose leg and being disposed outside the cassette, the displaceable hose leg latching in the operating position. Basically, both hose legs may be held in a displaceable manner. In conjunction with other functions possibly to provide, it is however recommended that only one hose leg is displace able between the mounting position and the operating position, and that the other hose leg is fixed in the longitudinal direction of the hose.
In principle, the enclosing angle of the hose around the roller wheel is arbitrary, as long as a sufficient crosssection reduction will result with corresponding tensional force on the hose in the area of a roller. It is preferred that the circular segment and thus the enclosing angle of the hose around the roller wheel will extend over at least 90xc2x0, preferably 170xc2x0 to 190xc2x0, most preferably 180xc2x0. It is suitable to form the hose at least in the area of the circular segment from a rubber-elastic material, in particular a natural or synthetic elastomer material, preferably a silicone caoutchouc or an elastomer polyurethane(co)polymer. The higher the modulus of elasticity, the lower the necessary tensional force at the displaceable hose leg.
In the embodiment with only one displaceable hose leg it is preferred that the fixed hose leg comprises a connection element having stop surfaces preferably extending orthogonally to the longitudinal extension of the hose, said stop surfaces resting against fixing surfaces in the cassette housing. By interaction of the stop surfaces with the fixing surfaces, the connection element and thus the hose leg are fixed virtually without any clearance. This embodiment permits that the connection element of the fixed hose leg comprises a pressure sensor communicating with the peristaltic pump, when the cassette is mounted at the peristaltic pump. The pressure sensor being in hydrostatic connection with a fluid flowing through the hose, may be adapted as a pressure transducer, the pressure acting on the sensor being transformed into an electrical value or an electrical signal, respectively. Communication with the peristaltic pump will then operate over complementary contacts at the pressure sensor and at the peristaltic pump. It is however also possible that the pressure sensor is adapted as a pressure membrane and is in mechanical connection with a pressure transducer provided in the peristaltic pump, when the hose cassette is mounted. This is particularly advantageous with regard to cost.
Preferably the displaceable hose leg is provided with a connection element comprising a latch element. In detail, the latch element may comprise a stop surface, by means of which for a cassette mounted at the peristaltic pump, a locking element provided at the peristaltic pump can be lifted, during the displacement of the displaceable hose leg, from the mounting position into the operating position against spring pressure from a locking position, and the latch element comprises adjacent to the stop surface a blocking surface in the direction of the operating position, the locking element engaging in its locking position behind said blocking surface. The particular advantage of this specific embodiment is that due to the arrangement of the blocking surface on one hand in the frame of the cassette and of the locking element on the other hand in the frame of the peristaltic pump, no special unlocking mechanism or no special unlocking handling is necessary when the cassette is removed from the pump housing. When, the cassette is removed from the pump housing, the locking element will come free from the blocking surface, with the consequence of release of the connection element and thus the relaxing of the hose by displacement of the displaceable hose leg into the mounting position. In the simplest case, the locking element is a locking pin.
Preferably the hose, possibly together with the connection elements, can be removed from the cassette housing. In detail: the cassette housing may have a substantially half-oval shape with two plane half-oval surfaces, one half-oval surface being closed and the opposite half-oval surface being open and comprising a cutout for engagement of the roller wheel. Through the open half-oval surface, the hose may be removed, if necessary together with its connection elements. Such an embodiment permits re-use of the cassette housing and thus a considerable reduction of waste. A rejected cassette is collected as waste and for instance returned to the manufacturer, who will then remove in a simple way the hose and the connection elements from the cassette, scrap those and take the cassette for renewed use.
The connection of the hose cassette to the peristaltic pump can be achieved in various ways. In any case it is a releasable connection. A preferred embodiment is characterized in that at least one form fit cutout is provided at a wall being orthogonal to the half-oval surfaces, and that spaced to the form fit cutout, in relation to the wall, at least one friction-drive element is provided, by means of said friction-drive element a releasable connection to the peristaltic pump being achieved by moving the friction-drive element in a direction being parallel to wall In this embodiment, application is as follows. An operator takes the cassette housing and puts it inclinedly in place at the peristaltic pump, thus establishing a form fit connection. After establishment of the form fit connection, the cassette in pressed in a tilting manner (axis of rotation at the form fit connection) to wards the peristaltic pump, thus the friction-drive connection being established, and the cassette is held safely in position at the pump housing.
The invention further relates to a peristaltic pump comprising a pump housing, a roller wheel projecting over the outside wall of the pump housing, and comprising a hose cassette according to the invention, wherein the connection elements being complementary to the connection elements of the cassette are provided at the outside wall. It is understood, herein, that the axis of rotation of the roller wheel is orthogonal to the outside wall and substantially coaxial with the circular segment. In a peristaltic pump according to the invention, various other functions may be covered by the hose cassette. The arrangement of a pressure transducer interacting with a pressure membrane, when the cassette is put in place, has been described above. Further it is possible that a drive motor of the roller wheel is controlled such that drive is only possible with mounted cassette. This can for instance be achieved by a switch or the like operated by the cassette put in place at the pump housing. A particularly advantageous embodiment is characterized in that for controlling the drive motor, a switching element is operable by the locking element. The switching element is activated in the locking position of the locking element, not however in a rest position obtained without mounted cassette. As a result, the roller wheel may only be controlled or rotationally driven, if (cumulatively) the cassette is mounted at the pump housing, and the displaceable hose leg is in the operating position.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is illustrated.